Effects of organic fractions on the formation and control of N-nitrosamine precursors during conventional drinking water treatment processes

Knowledge of N-nitrosamine precursors from dissolved organic matter (DOM) is important for water professionals to better control N-nitrosamine formation. The characterization of DOM from the Luan River in Northern China was conducted using Amberlite XAD resins and ultra-filtration methods. N-nitrosamine formation potentials were investigated for various DOM fractions. The removal of the DOM during water treatment were evaluated using dissolved organic carbon (DOC) and ultraviolet absorbance at 254 nm (UV254) bulk parameters as well as size exclusion chromatography and fluorescence spectroscopy. The results indicated that the XAD-4 hydrophilic fraction, with normalized yields of N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR), and N-nitrosopiperidine (NPIP) of 27.2, 5.2, 5.9, and 6.1 ng/mg-DOC, respectively, tended to form more N-nitrosamines than the hydrophobic and the transphilic fractions. The DOM fraction with a molecular weight (MW) below 1 kDa, with normalized yields of NDMA, NPYR, NMOR, and NPIP of 39.6, 8.1, 14.7, and 3.3 ng/mg-DOC, respectively, tended to form more N-nitrosamines than those with a higher MW. The limited removal of the hydrophilic fraction and the lower MW DOM faction during conventional water treatment processes suggests that the process may not effectively remove the nitrosamine precursors.

► Hydrophilic organic formed more NDMA and other nitrosamines than hydrophobic and transphilic ones.
► Small MW organic (< 1 k) formed more N-nitrosamines than those with larger MW.
► NDMA, NPYR, NMOR, and NPIP precursors were found in high level in this source water.
► Traditional process removed less hydrophilic and small-MW organic fraction.
► Traditional process is not effective in reducing the N-nitrosamines precursors.